1. Field of the Invention
This invention relates to a focal-plane shutter for cameras.
2. Description of Related Art
Shutters for cameras are roughly divided into two classes, focal-plane shutters and lens shutters. Focal-plane shutters used in recent years are mainly provided with two shutter blades (a first blade (group) and a second blade (group)), which are separately placed in two blade chambers constructed with three plate members, called a shutter base plate, an intermediate plate, and an auxiliary base plate, respectively. The shutters of this type are used in film cameras and digital cameras as well, and the two shutter blade groups are actuated in turn at a preset interval of time in photography so that an exposure operation is continuously performed, through a slit provided by the shutter blade groups, from one side of a rectangular imaging surface toward its opposite side.
Some of focal-plane shutters used only in digital cameras have a single shutter blade group. In this case, of the three plate members, the intermediate plate is not provided and the shutter base plate and the auxiliary base plate constitute a single blade chamber. In the shutters of this type, the imaging surface is usually exposed to light from an object, and only when photographing is completed, the imaging surface is temporarily covered.
In both types mentioned above, however, the shutter blade groups have the same structure, each with a mechanism in which one or more strip-shaped blades are supported to be rotatable with respect to a plurality of arms whose ends are pivotally mounted to the shutter base plate and thereby a link mechanism of parallelogram is applied. This pivotally supporting structure with the arms and the blades is such that holes provided in the arm and the blades are superposed and the tops of joint shanks which are rivet parts are inserted into the holes from the arm side and are caulked to the blades. The shutter is designed so that each of caulking portions does not project from the sliding surface of the blade in accordance with the shape of the blade, but the head of the joint shank, situated on the shutter base plate side or the auxiliary base plate side, projects from the arm.
The lens shutters, on the other hand, are of two types: a lens shutter located between two photographic lenses and a lens shutter located behind them. Most of such lens shutters are such that an exposure aperture is opened and closed at about the middle thereof. In either type, the lens shutters can be used in both film cameras and digital cameras. When they are used in the digital cameras, the imaging surface is usually exposed to light from the object, and only when photographing is completed, the imaging surface is temporarily closed.
Moreover, some of the lens shutters have an aperture restriction as in a stop mechanism. In this case, when they are used in the film cameras, a closing operation is performed from a preset position of the aperture restriction before a circular exposure aperture is fully opened in photography, while when used in the digital cameras, the aperture is opened at a preset position of the aperture restriction before photography, and the closing operation is temporarily performed only when photographing is completed. Even in such lens shutters, blades and members actuating the blades are connected by fitting structures that the joint shanks inserted into the holes can be rotated.
The shutter mechanism constructed as mentioned above is operated at fairly high speed, and thus the shutter appears to work and stop without any problem. In practice, however, the shutter is operated with complicated movement, as the case may be, and experiences a serious shock when stopped, so that, for example, the blades are temporarily deformed. Consequently, extremely fine wear dust is produced by sliding and abutment due to movements of individual members. Such wear dust may be produced even where one surface slides over another surface as in the blades or the blade and the base plate, but most often where the shank slides along the hole as in a portion connecting the blade to another member.
A typical example of the above description in the focal-plane shutter will be explained below. An ordinary shutter blade group, as mentioned above, is constructed with the arms, blades, and joint shanks. As such, in the operation of the shutter blade group, the fitting portion in which the joint shank is inserted into the hole of the arm is relatively brought into a sliding and contacting state. The impact force exerted by the stop of the shutter considerably influences this fitting portion. Moreover, in the operation of the shutter blade group, the heads of the joint shanks slide over the surface of the base plate. In this operation, not only is the shutter blade group normally actuated, but it is irregularly moved. In particular, since the arms and the blades are deformed at a stop, the phenomenon occurs such that the heads of the joint shanks are struck against the surface of the shutter base plate or the auxiliary base plate. Furthermore, in most cases, the pivotally supported portion of a slit-forming blade is constructed to enter and leave the exposure aperture in the operation of the shutter blade group, and thus when it leaves the exposure aperture, the heads of the joint shanks abut on the edge of the aperture of the shutter base plate or the auxiliary base plate.
This will be explained with reference to a conventional example shown in FIG. 1. In this figure, an aperture Aa is provided at about the middle of a shutter base plate A. Although this conventional example is actually provided with two shutter blade groups, only the second blade group is shown in FIG. 1. Thus, in the conventional example, an intermediate plate B is placed on the back side of the shutter base plate A, and an auxiliary base plate C is also placed on the back side thereof, so that the second blade group is situated in a blade chamber provided between the intermediate plate B and the auxiliary base plate C. Apertures Ba and Ca, similar in shape to the aperture Aa, are provided in the intermediate plate B and the auxiliary base plate C, respectively, and the shape of the exposure aperture (an image frame) is restricted by at least one of these apertures.
The second blade group is constructed with two arms D and E and four blades F, G, H, and I. The arms D and E are rotatably mounted to the shutter base plate A at their left ends, and the blades F, G, H, and I are pivotally supported with respect to the arms D and E through the joint shanks (rivet parts). The pivotally supporting structures of individual blades are the same, and hence only the pivotally supporting structure of the blade I will be described here. A joint shank J is inserted into the holes of the arm D and the blade I from the side of the auxiliary base plate C, and the end of the inserted shank is caulked to the blade I. A joint shank K is also inserted into the holes of the arm E and the blade I from the side of the auxiliary base plate C, and the end of the inserted shank is caulked to the blade I. Consequently, the heads of the joint shanks J and K are situated on the side of the auxiliary base plate C, and the arms D and E and the joint shanks J and K are not fixed. The caulking portions of the joint shanks J and K, not shown in the figure, are such that they do not project into the surface side of the blade I (this side of the paper of FIG. 1) by partially deforming the blade I.
In the structure mentioned above, when the second blade group is actuated, the joint shanks J and K follow arcuate working paths indicated by chain lines in the figure. Since the remaining six joint shanks are also operated at the same angle, their working paths likewise become arcuate. In this operation, the blades F, G, H, and I, in which a mutually overlapping relation is changed, slide along adjacent blades. The blades F, G, H, and I also slide along the intermediate plate B and the auxiliary base plate C. On the other hand, individual joint shanks slide in the holes of the arms D and E, and the outer surfaces of their heads slide over the auxiliary base plate C. In most cases, however, the heads of the foremost joint shanks J and K of the arms D and E abut temporarily on the edge of the aperture Ca or at a portion close thereto in the operation process of the shutter. Hence, such sliding and abutment are responsible for the production of wear dust. It is needless to say that this holds for the case of the first blade group interposed between the shutter base plate A and the intermediate plate B.
The arms and blades mentioned above are ordinarily manufactured in such a way that thin metallic plates with relatively high rigidity are blanked by a press machine. The joint shanks, as the rivet parts, are manufactured by cutting bar stocks of free-cutting steel. Consequently, even when the shutter blade group is constructed with a plurality of blades, the frequency that wear dust is produced by sliding of blades is extremely diminished. In addition, even in the case where the blades slide along plate members constituting the blade chamber, sliding and contact between relatively large surfaces are brought about, and hence the wear dust is rarely produced even though the plate members are made of synthetic resin (the shutter base plate and the auxiliary base plate are sometimes made of synthetic resin).
In the fitting portion in which the joint shank is inserted in the hole of the arm, however, the joint shank may be worn to produce relatively many particles of wear dust. Where the shutter base plate and the auxiliary base plate are metallic, relatively hard metal is used, and thus the heads of the joint shanks may be worn by sliding and abutment relative to them to produce relatively many particles of wear dust. Moreover, when the shutter base plate and the auxiliary base plate are made of synthetic resin, wear dust may be produced from these base plates. The lens shutter, although different in structure, is also provided with fitting portions in which the joint shanks are inserted into the holes and has a plurality of sliding and contact portions. Hence, the lens shutter will produce such wear dust to a greater or less degree.
It is desirable that, even through the wear dust is produced as described above, provision is made for driving the wear dust in a direction different from that of the exposure aperture so that the dust does not reach the imaging surface of a film or a CCD through the exposure aperture. However, such favorable provision is not easily available. In particular, since as mentioned above the joint shanks J and K situated at the foremost ends of the arms D and E are operated inside the exposure aperture, it is extremely difficult that provision is made to prevent wear dust produced by at least the joint shanks J and K from adhering to the surface of the film or the CCD.
If such wear dust adheres, over a preset amount, to the surface of the film or the CCD, a favorable photographing result will not be obtained, and when an image is magnified and reproduced, a part of the image develops a defect. In particular, the digital camera is such that an image sensor is fixed in the camera, and thus when the wear dust adheres directly to the entrance surface of the image sensor or a low-pass filter disposed in front thereof, the influence of the dust is exerted on any subsequent photography and additional particles of wear dust adhere successively to and around the surface. This causes a serious problem.
Thus, in a conventional case, when such a phenomenon is brought about in the camera equipped with the focal-plane shutter, a lens is removed, a mirror is raised up, the shutter blade group is moved from the front of the image sensor (the exposure aperture is brought into a fully opened state), and then wear dust must be eliminated by an air brush. However, this work is by no means easy, and in a camera which is not designed to interchange lenses such as that provided with a zoom lens or a lens shutter, even the above way cannot be adopted. The same holds for provision to eliminate dirt entering a camera from the exterior or produced in the camera, as well as the wear dust. Therefore, the advent of a new shutter for cameras with little influence of the wear dust or dirt is hastened.
On the other hand, in the film camera, even though the wear dust adheres to the film in such a manner as mentioned above, the frame of the film is changed each time photographing is performed and thus the dust merely adheres to each frame. It is impossible that the dust is accumulated and attached as in the digital camera. Hence, the wear dust has little been regarded as a problem. However, since it has been thought of as a problem in the digital camera, a demand has recently been increased for a new shutter in which the above phenomenon is hard to occur even though it has a slight influence on the shutter.
It is, therefore, a primary object of the present invention to provide a focal-plane shutter for cameras in which it is avoidable that the heads of joint shanks situated at the pivotally supporting portions of the arms and blades of the shutter blade groups abut on the edges of the apertures of the base plates constituting the blade chambers or on portions close thereto to produce wear dust.
It is another object of the present invention to provide a focal-plane shutter for cameras in which wear dust produced by the operations of the shutter blade groups and dirt existing in a camera are hard to reach the imaging surface through the exposure aperture.
It is still another object of the present invention to provide a focal-plane shutter for cameras in which a dimension in the direction of the optical axis in a camera can be reduced.
In order to achieve the above objects, the focal-plane shutter for cameras of the present invention is provided with a single blade chamber between two base plates, each having an aperture for exposure at about the middle thereof, or two blade chambers into which the single blade chamber is partitioned between the two base plates by an intermediate plate having an aperture for exposure at about the middle thereof. A shutter blade group placed in each of the two blade chambers is constructed with a plurality of arms whose ends are pivotally mounted to one of the two base plates at the side of the aperture and at least one blade pivotally supported by the arms through individual joint shanks so that working paths of the joint shanks does not run inside the apertures of the base plates. In addition, a wall is provided on at least one of the two base plates so as to project toward the blade chamber side, between the aperture provided in one of the two base plates and the working region of the arms, along the edge of the aperture. When the wall has an inclined face directed toward the aperture of an opposite base plate, light reflected by the wall becomes hard to reach the imaging surface. In this case, when the inclined face is configured and thereby the dimension of the end face of the aperture in a direction parallel with the optical axis is made smaller than the thickness of the base plate provided with the inclined face, the effect of the present invention is further heightened.
In the focal-plane shutter for cameras of the present invention, when the wall is provided to extend to the outer edge of the base plate, the wear dust becomes hard to reach the imaging surface.
In the focal-plane shutter for cameras of the present invention, when the wall is integrally molded out of synthetic resin or is configured through the knockout process and press process of a metallic plate, fabrication is facilitated.
In the focal-plane shutter for cameras of the present invention, when the intermediate plate is mounted to partition the single blade chamber between the two base plates so that it is not moved relative to the two base plates, the function of the wall is more effective than in the case where it is moved.
In the focal-plane shutter for cameras of the present invention, when the shutter blade group has a plurality of blades and the wall provided on the side of the blade chamber of the shutter blade group is configured so that the amount of projection is increased in the direction in which the blades of the shutter blade group are spread, the wear dust becomes hard to reach the imaging surface even when the shutter is downsized.
In the focal-plane shutter for cameras of the present invention, when adhesive substances are applied to or stuck on faces of the wall located on the side of the working region of the arms, the wear dust adheres thereto so that it is not scattered. In this case, when the adhesive substances are also used as antireflection substances, this is advantageous for light-leakage prevention.
In the focal-plane shutter for cameras of the present invention, when the base plate placed on the imaging surface side has a concavity for receiving a part of a lowpass filter or image sensor so as to surround the aperture on the imaging surface side, this offers the advantageous of reducing the thickness of a digital camera.
The focal-plane shutter for cameras of the present invention is provided with a blade chamber between two base plates, each having an aperture for exposure, to place a shutter blade group in the blade chamber, or two blade chambers into which the blade chamber is partitioned between the two base plates to place a different shutter blade group in each of the two blade chambers. In this case, at least one of the two base plates is provided with adhesive means on surfaces with which the shutter blade group has no contact to operate.
In the focal-plane shutter for cameras of the present invention, when the adhesive means are provided in troughs configured on at least one of the two base plates, the adhesive means can be easily placed in the working region of the shutter blade group when the troughs are configured in the blade chamber. Moreover, when they are configured outside the blade chamber, accessibility of the adhesive means is reduced, and thus this is advantageous for handling of the shutter.
In the focal-plane shutter for cameras of the present invention, when a frame is configured so as to surround the aperture, outside the blade chamber, on at least one of the two base plates and is provided with the adhesive means, wear dust or dirt scattered from the interior of the blade chamber toward the object side is easily captured and the amount of dust which reaches again the interior of the shutter can be reduced.
In the focal-plane shutter for cameras of the present invention, when at least one of the two base plates has a wall extending from the aperture to its peripheral ends on the blade chamber side and is provided with the adhesive means on at least one of a surface on the blade chamber side and a face of the wall which is not parallel with the surface, wear dust or dirt is easily captured effectively and becomes hard to reach the aperture side.
In the focal-plane shutter for cameras in this case, the shutter blade group has a plurality of arms rotatably mounted to one of the two base plates and at least one blade pivotally supported by the arms, and the wall is interposed between the working region of the arms and the aperture. By doing so, the structure becomes entirely favorable for the focal-plane shutter.
In the focal-plane shutter for cameras, when the adhesive means has an antireflection function, this is advantageous for light-leakage prevention.
These and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.